Energy generator for cathode ray deflection means



Jan. 7, 1941. ANDR|EU 2,227,480

' ENERGY GENERATOR FOR CATHODE RAY DEFLECTION MEANS Original Filed Nov. 7, 1936 2 Sheets- Sheet l DfiZtZf/NG if v INVENTOR 19049.50 Amok/EU DEFECT/N6 ATTORNEY Jan. 7, 1941. ANDRIEU 2,227,480

ENERGY GENERATOR FOR CATHODE RAY DEFLECTION MEANS Original Filed Nov. 7, 1936 2 Sheets-Sheet 2 DEFLECTIIYG 65/4 DEFLECTIIYG C014,

INVENTOR ROBERT AWBR/EU ATTO'RN EY Patented Jan. 7, 1941 PATENT OFFICE ENERGY GENERATOR FOR CATHODE RAY DEFLECTION MEANS Robert Andrieu, Berlin, Germany, assignor to T'elefunken Gesellschaft fiir Drahtlose Telegraphic in. b. H., Berlin, Germany, a'corporation of Germany Application November 7, 1936, Serial No. 109,623 Renewed May 10, 1939. In Germany October 28,

12 Claims. (01. 250-36) In television practice the transmitter, as Well as receiver, uses deflecting means for the cathode ray in the horizontal and the vertical coordinate of the television image. Ordinarily, deflection fields are used which for each image line have the same value. This is true for instance in case of an ordinary Braun tube employed as a television receiver. The fluorescent screen therein is arranged at right angles to the tube axis, 1. e. its center is impinged at right angles thereto by the axis of the cathode ray unless the latter is deflected, and the image lines'must of course, therefore, all appear with the same length. If, however, the flat fluorescent screen of a Braun tube is inclined with respect to the tube axis, for purposes of convenience in projecting the image formed on the screen, for instance, or for direct viewing on an angle to the axis of the tube, it-is not possible for all lines to be formed of the same length by the same value of deflecting field. The individual image lines must have the same length on the fluorescent screen and this result can be accomplished only if during the line deflection of the cathode ray care is taken that the cathode ray beam is subjected to a non-constant deviation. If for each line the cathode ray were to be deflected by the same field, the lines nearer to the deflecting devices of the Braun tube would be traced too short and the lines further removed would become too long. Thus the receiving image would have the form of a trapezoid. Therefore, it is necessary to vary from line to line the amplitude of the line deflection in order that a rectangular image surface is traced on the inclined fluorescent screen. The deflection field which produces the deflection in the direction of the line, must, therefore, have an intensity that is the higher the nearer the respective part of the fluorescent screen is situated'with respect to the deflection devices of the tube. Under such condition the cathode ray would describe a trapezoidal image field on a surface positioned at right angle to the axis of the Braun tube. A trapezoidal deflection in the sense explained is also required, for cathode ray type image scanners in which the screen to be scanned is obliquely arranged with respect to the axis of the scanning ray tube. 'A1so,'a trapezoidal ray deflection may also be useful in fields of application outside of the televisionfield.

The present invention has for its object to produce saw tooth current of a wave shape necessary for the trapezoidal deflection of a cathode ray beam where electromagneticcoils' are used. In accordance with the invention this is' accomplished byv providing a potential always having the same sign and of the proper frequency for reconstructing an image linearly. The saw tooth shaped wave is applied to the deflecting apparatus whichforms-a part of an oscillatory circuit which preferably consists of the inductance and distributed capacity of the deviation coil, or coils, whereby the said voltage is applied during the long flanks of the saw-tooth current curves and is interrupted for each short flank.

The invention will best be understood with reference to the drawings in which:

Figure 1 is an arrangement of the prior art.

Figure 2'is an explanatory curve.

Figure 3 is one embodiment of my invention.

Figure .4 is an explanatory curve.

Figure 5 is an explanatory trapezoid.

Figure 6 isan explanatory trapezoid.

Figure 7 is another embodiment of my invention.

Figure 8 is a set of explanatory curves.

Figure 9 is another embodiment of my invention.

Figure 10 is still another embodiment of my invention'.

Figure 11 is a set of explanatory curves.

Figure 12 is another modification of my invention.

Figure 13 is a set of explanatory curves.

Figure 14 is an embodiment.

Figure 15 is a set of explanatory curves.

Figure 16 is a modification of the circuit shown in Fig. 14.

Figures 17 and 18 are a set of explanatory curves; and

Figure 19 is another embodiment of my invention.

Before explaining these modes of construction in accordance with my invention, the production of the current curves for the line deflection will be explained in connection with Fig. 1 whereby it is assumed that the amplitude of the saw-tooth current has the same value for each line, i. e. it is presupposed that a rectangular surface is to be scannedon ascreen extending at right angles to the axis of the cathode ray tube.

Referring to Fig. 1, l0 designates a multi-grid tube i. e. a tube having a very high inner resistance, I I is a cathode ray beam deflection coil, I2 is a detector, and I3, I l designate direct voltage sources. In order to explain the performance of this arrangement it is assumed that the tube In is conducting during'the duration of the line signals, and non-conducting during the line pause. To this end, during each line pause a negative impulse is applied to the control grid of the tube It, while within the duration of the line a positive (or less negative) grid potential I6 is supplied to said grid.

Referring to Fig. 2, it is assumed that at the moment iii, in which the tube l0 permits the passage of current, the deviation coil II is energized by a current having the value i1 while a current Io passes through the tube It, so that" the detector conducts a current in. The coil II has the constant voltage l3 so that the current in this coil must increase by a tangent determined by the value of this voltage. At the moment t2 (coil current i2) the current passage through the tube III will be blocked and thus the current across the detector l2 will be interrupted simultaneously. The deflection coil ll then performs a free half oscillation, within which the current i2 varies up to the value is. Shortly after the moment its in which the current value is is attained, a voltage difierence is developed across :the coil I I vwhich with respectto the detector I2 has the opposite direction and a higher value than the voltage source 13, so that the detector l2 again permits the passageof current. From this moment the voltage I 3 lies again at the choke coil ll across detector. 12, so that the current by means of the choke coil must vvary again in accordance with. a .tangent whose value depends upon the value of the voltage [3. Furthermore, shortly after the time is the tube Illv will again be rendered conducting so that the current In flows again until at the time t; the tube II] will be blocked again. The current in acrossthe detector during the long-flank of the saw-tooth curve is represented by the ordinates of the shaded surface in Fig. 2. This current is independent of the steepness of the long flanks as long as is is smaller than Io. In the circuit shown in Fig. 1,

40 the feature especially notable in connection with the invention to be explained hereinafter, resides in that the tangent of the current increase in the deflection coil H solely depends on the value of the voltage I3.

45 The production of saw tooth shaped current curves whose amplitude varies in proportion to time such'as required for the trapezoidal deflection, is thus possible by taking care that the voltage 13 whose sign must always be the same,

' is varied in the rhythmof the. desired cycle of the trapezoid. In. fact, if thisvoltage I3 during the production of a single current saw tooth, according to Fig. 2 is higher or lower than during the production of the preceding saw tooth, dur- 55 ing the respective line the tangent on the current curve and therefore the amplitude of the saw tooth is higher or lower than during the preceding line.

Referring to Fig. 3 which shows one embodi- 60 ment of my invention, the voltage taking a saw tooth shaped course with the desired cycle of the trapezoid is formed by the direct voltage source l3 and an alternating voltage source of saw tooth shape connected in series to said source 5 l3. This alternating potential source may consist, for instance, of a transformer ll whose secondary winding is connected in series with the detector l2 and the direct voltage source l3, and whose primary winding is energized by a 70 current whose curve form is a parabola. Such parabolic current may be produced forinstance by controlling two parallel connected thermionic tubes having a performance characteristic of different steepness, .with two saw tooth voltages in 75 phase opposition. If the voltage supplied by the transformer I1 has the course indicated by Z (see Fig. 4), a trapezoid according to Fig. 5 will be traced i. e. the value of the line deflection increases within the duration of the trapezoid. If care is taken that the saw tooth voltage de- 5 scribes a course according to the curve Z, such as can be readily accomplished by a corresponding polarization of the secondary winding of the transformer ll, or through corresponding choice of the direction of its primary current, a trapel0 zoid according to Fig. 6 will be described 1. e. the length of the lines decreases during the tracing of the trapezoid. The curves of Fig. 4 would, of course, be of frame frequency.

In the examples of construction to be described 15 in the following for the production of the saw tooth voltage a condenser is charged during the formation of the trapezoid with a constant current whose direction of charge is opposite to that prevailing during the interval between the trape- 20 zoid.

Referring to Fig.7, this condenser .is designated by I8, a resistor in parallel thereto is designated by l9. Adirect voltage source 20 is placed in series to the condenser resistance members I8, I 9 and the detector. In explaining the operation of the arrangement accordingto Fig. 7,,reference should be had to the curves shown in Fig. 8. In Fig. 8 the voltage 20 is designated by UAC. R. represents the voltage drop at resistor I9 which would appear if the voltage shown at the control grid in Fig. 1 were continuously, acting upon the control grid of tube I0. However, during the trapezoid intervals negative voltage impulses act upon the control grid of tube ID, a saw tooth shaped voltage always having the same sign will be produced between the points A andB. The short negative impulses I5 may be neglected for the following considerations, and it be thus assumed that the tube In permits the passage of currentfor the entire duration of the trapezoid. The voltage IR corresponds to the state of charge of the condenser at which the entire detector current passes across the resistor R, and the condenser charge has become a constant charge. It

' is assumed that at the time its (the beginning of the trapezoid) the voltage dropIs. R may exist at the resistor l9, and is lower than the voltage drop LR, and that the tube It) permits passage of current. The current passing across the detector l2 will be branched off at the point C, partially charging the condenser l8 and passes across the resistor I9. If at tube I 0 no negative impulse according to that during the trapezoid interval would appear, the condenser will finally be fully charged to the voltage LR, and consequently a branching of the current 'nolonger takes place at the point C but the entire current I passes across resistor R. Through suitable dimensioning of the, time constants of the resistor-l condenser members I 8, 19 it can be arranged that this state will not be reached before a time period equal to a multiple of the duration of the trapezoid has elapsed, so that,'therefore, from is to is which is the beginning of the following trapezoid interval, no variation in the charge of the condenser, and hence no variation in the voltage drop at resistor l9 occurs. The variation in the charge takes place in accordance with an e-function, if as, already stated above, the influence due to the short negative impulses 15 upon the increase in charge is disregarded. At the time to the tube I0 will be blocked, so that the'current I disappears. Now, the condenser [8 will be discharged across the resistor IS, in accordance-with the exponential function which approaches the end state of the voltage "drop at resistor 19, i. e., the voltage UAG at the coil I. This end state would however likewise be attained only after a mul- 5 tiple of trapezoid intervals. However, after a comparatively short time, namely, at the time t7 the tube Ill is again pervious to current so that the charge of the condenser Hi again begins to increase, again approaching the end value IR. At the time is a new trapezoid pause begins, within which there takes place again a partial discharge of the condenser l8. Thus a saw tooth shaped voltage UAB having always the same sign,

appears between the points A and B such that the potential at the'point B is always lower than .the potential at point A.

Hence in order to produce the trapezoidal deviation with the circuit according to Fig. I, it is only necessary to apply to the grid of tube 20 I0 (aside from the short impulses It in Fig. 1)

impulses in the direction of the blocking during the trapezoid pauses. As explained, the sawtooth formed voltage in series to the detector I2 is then produced through charging of the con 5 denser I8, within the duration of the trapezoid and of the trapezoid interval with currents having opposite direction.

As already pointed out, the increase in the charge of the condenser i8 takes place in accord- 30 ance with an e-function i. e. in accordance with a curved course, and, furthermore, a very high voltage 20 is required depending on the coil used and on the line frequency. To avoid these disadvantages, in other words, in order to attain a very high time constant and therewith a linear voltage increase, and in order to provide a decrease at any event in the high voltage 20 or to be able to dispense therewith, the resistor l9 may be replaced by a multi-grid tube'such as a screen 40 grid tube for instance. The correspondingcircult is shown in Fig. 9 in which the screen grid tube is designated by 2|. The voltage 22; is lower than in the case of Fig. .7. The functioning is similar to that described in connection with Figs.

"45 '7 and 8.

.55 the trapezoid.

In the circuit shown in Fig. 10 the screen grid tube 2! is used. In addition to a negative bias potential source 22 in the control grid circuit there is placed also the secondary winding of a no transformer 23. To explain the functioning let it be at first assumed that at the time is in Fig. 11a (the beginning of the duration of a trapezoid) the condenser 18 may have a voltage with the signs as shown in Fig. 10, and which is higher 65 than the voltage Trio of the direct voltage source 20. The tube I0 is conducting, whereas the tube 2| is blocked in view of the negative grid, bias potential 22. To constant current 2'0 passing across the detector l2, therefore, increases the 70 voltage at the condenser up to the moment is i. e. at the beginning of the trapezoid pause a positive voltage impulse passes across the transformer 23 to the control grid of tube 2|. The tube 2| permits passage of current 'and'conducts a constant -,15 current up to the time it (at the beginning of the following duration of the trapezoid). Therefore, the voltage at the condenser decreases during the pause of the trapezoid. At the time t7 the tube 10 will again be opened and the tube 2| closed again so that a new charging performance '5 for the condenser M! will be initiated. Figure 111) shows the course of the current during this time. Herein is in the current in the detector l2, which as already stated also flows during the trapezoid interval. During the time in which the tube 2| 10 is blocked this current in charges the condenser (thus still designated it; in Fig. 10b) while during the trapezoid interval a current is flows charging the condenser l8 across tube 2|. The shaded surfaces above and below the zero line are equal to each other.

In the circuit shown in Fig. 10 a certain disadvantage resides in that the condenser |8 must be discharged during the short trapezoid interval across the tube 2|. For this reason in the practical construction comparatively large screen grid tubes must be employed. This disadvantage can be overcome and smaller screen grid tubes are sufficient if in addition to having the tube 2| conducting current only inv the trapezoid interval I25 this tube is also not completely blocked during the duration of the trapezoid. The circuit arrangement distinguishes itself from that according to Fig. 9 in that the bias potential of the tube 2| is less negative or zero. This latter case is shown in Fig. 12. In this case the current passes during the trapezoidinterval onlypartially across the condenser l8 so that with the same voltage variation the latter may have a lower capacity at the duration of the trapezoid. Hence also during the trapezoid interval only a smaller charge is to be removed, and thus a smaller tube 2| required. The Voltage course is the same as in Fig. 11a, the current course is shown in Fig. 13. The current in flows continuously and also the charging :40 current in for the condenser. The difference is between in and ic passes across the tube 2|. During the trapezoid interval the condenser will be discharged across the tube 2| with a current wherein P and D designate the ratio between trapezoid interval to trapezoid duration. The shaded surfaces above and below the zero line are again the same with respect to each other.

In the last mentioned mode of construction certain difliculties appear owing to the application of the voltage impulse to the control grid of tube 2| by means of transformation. In fact, it is rather difiicult to supply a high potential across the transformer 23 during the trapezoid interval, and to maintain the secondary voltage of the transformer exactly at the zero value or at a constant value during the duration of the trapezoid. 69

This disadvantage is avoided in two further modes of constructions, both having in an additional current branch a controlled tube, this current branch containing also the storage condenser. In view of the fact that the cathode of 6 this tube is not maintained at an alternating potential, the control impulse can be applied to this tube across a coupling condenser.

Referring to Fig. 14, between the point B and the negative pole of the plate potential source M 70 a controlled tube 24 is inserted which may for instance also be a screen grid tube which is blocked during the duration of the trapezoid. The screen grid tube 2| carries always the same current during the duration of the trapezoid and .175

the trapezoid interval. Fig. 15a shows the voltage course at the condenser E8, the point B being maintained always at negative potential with respect to point A. During the duration of the trapezoid the condenser 18 will be discharged with constant current across the tube 2| while the tube 24 permits the passage of current. During the trapezoid interval the current remains unchanged in the tube 2|, but a circuit from the positive pole of the plate voltage source l4 across the voltage source 28, condenser l8, anodecathodepath of tube 24, and back to the negative pole of the voltage source it will be closed by a corresponding impulse at the grid of tube 24. A charging current for the condenser 18 then passes across this circuit so that the voltage thereat increases again. The appertaining current course is shown in Fig. 15b. The current in and also the current is pass during the duration of the trapezoid and the trapezoid interval. The condenser current is has, during the duration of the trapezoid, a direction opposite to that of Figs. 10 and 12. In the same manner the charging current ia passing across the tube 28 during the trapezoid interval has the direction opposite to the current passing during the trapezoid interval in accordance with Figs. 11b and 13. The shaded surfaces above and below the zero line are again equal to each other.

It should be emphasized that as can already be derived from Fig. 14a a trapezoid according to Fig. 6 can be produced with the circuit according to Fig. 13, while the circuits according to Figs. '7, 9 and 11 produce a trapezoid according to Fig. 5. As shown in accordance with Figs. 8 and 11a the condenser charge increases in fact during the duration of the trapezoid, while decreasing according to Fig. 14a within the duration of the trapezoid. A controlled tube in the sense of tube 26 in Fig. 14 can be operated also in such manner that it is blocked during the trapezoid interval, while being maintained open during the duration of the trapezoid. The respective circuit differs from that in Fig. 14 only insofar as the tube 24 has a lower negative bias potential, as shown in Fig. 16. The condenser I8 will be charged during the duration of the trapezoid across the tube 20 which in this case is suitably a multi-grid tube, and the discharge takes place during the trapezoid interval across tube 2!. This discharge current passes also across the tube 2! during the duration of the trapezoid, however, in View of the current passing across tube 2d, the condenser charge decreases only during the trapezoid interval. Furthermore, the constant detector current i flows across tube 2|. In this arrangement a trapezoid according to Fig. will be produced.

In all forms of construction hitherto described it has been presupposed that the condenser in be constant during the duration of the trapezoid. This requirement is not exactly fulfilled owing to the finite resistance of the tubes for the alternating plate currents, although the resistance is high. However, in accordance with a further feature of the invention, a constancy of the condenser current, i. e. an increase in the time constant of the voltage course at the condenser can be attained during the duration of the trapezoid in that one of the tubes which determine the time constant is controlled in phase opposition to its alternating plate potential.

This will be explained in the following solely with reference to the form of construction of Fig. 14.

The current ie in Fig. 15b increases in the case of a constant voltage, at the control grid of tube III as represented in Fig. 17 for instance in accordance with the line is, since the charge of the condenser I3 decreases during the duration of the trapezoid. This causes a decrease of the current. across tube 2| thus leading to a current as designated by is. The condenser current thus has a course according to the line i0 during the duration of the trapezoid. A condenser current that is constant as regards time, can only be produced if care is taken that the current passing across the detector takes its course in accordance with the line i0 in Fig. 18. In considering the decrease of is then to can carry out the desired constant course in the trapezoid interval.

A circuit arrangement for the production of a voltage at the screen grid of tube [0 and which decreases in the course of the duration of the trapezoid, is represented in Fig. 19. The screen grid of tube I0 is connected across a coupling condenser 25 to the anode of a triode 26, in whose plate circuit a resistor 21 is inserted, and whose plate potential is likewise furnished by the plate voltage source M of the screen grid tube ID. A sawtooth formed voltage having the frequency of the trapezoid and slow increase and rapid decrease is applied to the control grid of the triode 26 across a coupling condenser 28. The control grid of the triode Z5 is hereby placed at the tap point of a potentiometer 29. The alternating plate potential appearing at the anode of the triode 26 is in phase opposition to the alternating grid potential of this tube, and, therefore, the screen grid voltage Whose direct voltage part is controlled by suitable setting of the potentiometer 30, will be decreased in such manner during the course of each duration of the trapezoid that the current course 2'0" in Fig. 18 appears.

Instead of controlling the tube ID in accord-' ance with Fig. 19, it is also possible to employ the course of the alternating voltage at condenser It for the control, through capacitive coupling.

What I claim is':

1. A sawtooth wave generator comprising means for storing electromagnetic energy, a discharge path for said energy, a source of constant bias voltage for said discharge path, and means connected in series in said discharge path for progressively supplementing said constant bias for a predetermined interval.

2. A sawtooth wave generator comprising a thermionic tube having anode, cathode and at least one control electrode, an inductive element joined electrically in the anode-cathode circuit of said tube, a discharge path for said inductive element, means for applying a constant biasing voltage in series in said discharge path, and

means for progressively supplementing said con-' stant biasing voltage for a predetermined interval of time.

3. A sawtooth wave generator comprising a thermionic tube having anode, cathode and at least one control electrode, an inductive element connected in the anode-cathode circuit of said tube, a unidirectional conducting device connected to said inductive element in a series circuit which is connected in parallel with said inductive element and forming a discharge path therefor, a source of constant potential connected to said discharge path, and means for progressively varying the biasing voltage on said discharge path for a predetermined period of time.

4. A sawtooth wave generator comprising means for storing electromagnetic energy, a thermionic tube having at least an anode and a cathode, said means for storing said electromagnetic energy being connected in the anode-cathode circuit of said tube, a uni-directional conducting device, a time constant circuit, and a source of energizing potential, said means for storing electromagnetic energy, said uni-directional conductor, said time constant circuit and said source of energizing potential being connected serially, whereby the energy stored in said electromagnetic energy storage means is progressively supplemented for a predetermined interval.

5. Apparatus in accordance with claim 4 wherein said uni-directional conductor comprises a diode.-

6. A sawtooth wave generator comprising means for storing electromagnetic energy, a thermionic tube including an anode and a cathode, said electromagnetic energy storage means being connected in the anode-cathode circuit of said tube, a source of steady biasing potential connected in the anode-cathode circuit of said tube and serially with said electromagnetic energy storage means, a uni-directional conductor, an inductive element, said electromagnetic energy storage means, said uni-directional conductor and said inductive element being serially connected, and means coupled to said inductive element for impressing thereon a signal to progressively supplement the constant bias for a predetermined interval.

'7. Apparatus in accordance with claim 6 wherein said thermionic tube is a triode.

8. Apparatus in accordance with claim 6 wherein said uni-directional conductor is a diode.

9. A sawtooth wave generator comprising means for storing electromagnetic energy, a first thermionic tube including an anode and a cathode, a source of constant energizing bias, said electromagnetic energy storage means and said source of constant bias being connected in the anode-cathode circuit of said thermionic tube, a uni-directional conductor, a condenser, a second thermionic tube having anode, cathode and at least one control electrode, said condenser being connected in the anode-cathode circuit of said second thermionic tube whereby said condenser is connected substantially in parallel with the spaced discharge path of said second thermionic tube, said electromagnetic energy storage means, said uni-directional conductor, and the parallel connection of the condenser and the second thermionic tube being connected serially, and means for impressing signals from an external source onto the control electrodecathode path of said second thermionic tube, whereby said constant bias is supplemented progressively for a predetermined interval.

10. Apparatus in accordance with claim 9 wherein the means for impressing signals from an external source onto the control electrodecathode path of said second thermionic tube comprises a transformer having the secondary thereof connected in the control electrode-cathode path of said second thermionic tube and the primary thereof energized by the signals from the external source.

11. Apparatus in accordance with claim 9 wherein said uni-directional conductor comprises a diode.

12. Apparatus in accordance with claim 9 wherein said second thermionic tube comprises a screen grid tube.

ROBERT ANDRIEU. 

